Reticulofenestra asanoi

Ancestry: Coccolithophores -> Isochrysidales -> Noelaerhabdaceae -> Reticulofenestra -> R. pseudoumbilicus group -> Reticulofenestra asanoi
Sister taxa: R. calicis, R. pseudoumbilicus, R. haqii, R. minuta, R. rotaria, R. minutula, R. asanoi,

Short diagnosis: Coccoliths >6.5µm, sub-circular or broadly elliptical.


Citation: Reticulofenestra asanoi Sato and Takayama, 1992.
Rank: Species
Notes & discussion: Probably derived from P. lacunosa, from which it is distinguished by the absence of slits in the distal shield.

Farinacci & Howe catalog pages: Reticulofenestra asanoi *

Short diagnosis: Coccoliths >6.5µm, sub-circular or broadly elliptical.

Geological Range:
Notes: Short interval within NN19
Last occurrence (top): within NN19 zone (0.44-1.93Ma, top in Ionian stage). Data source: Young 1998
First occurrence (base): within NN19 zone (0.44-1.93Ma, base in Gelasian stage). Data source: Young 1998

Plot of occurrence data:


Sato, T. & Takayama, T., (1992). A stratigraphically significant new species of the calcareous nannofossil Reticulofenestra asanoi. In: Ishizaki, K. and Sato, T. (Editors), Century of Japanese Micropalaeontology. Terra Scientific Tokyo, Tokyo, pp. 457-460.

Young, J.R., (1998). Neogene. In: Bown, P.R. (Editor), Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publications Series. Chapman & Hall, London, pp. 225-265.

Nannotax3 - Coccolithophores - Reticulofenestra asanoi by: Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 28-4-2017

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Mike Styzen (Noble Energy, US)
I've never been able to really embrace this species as I need some definite criteria for distinguishing it absolutely from Pseudoemiliania ovata on the one hand and any number of medium sized nondescript Reticulofenestras on the other. I've been told that R. asanoi may not be totaly devoid of slits on the distal shield, it may have a few. If this is the case what makes it different from just a big P. ovata? Is there a cutoff size? Other features to watch for?
Jeremy Young (NHM, UK)
I must admit I have had problems with this too. I tried arguing a long time ago (Young 1991) that we ought to get rid of Pseudoemiliania since it intergrades with Reticulofenestra, and the existence of R. asanoi makes it even worse. The best study I know of the group is still Matsuoka and Okada (1989) they used TEM to measure and count specimens, which is a good way to reliably spot the slits and give detailed data on morphotypes in the group in the mid Quatnary from a piston core in subtropical N.W. Pacific.
They defined a Reticulofenestra sp. A , >5µm with no slits and showed that the >6µm examples of this morphotype had a limited range around the Jaramilo magnetochron (C1r.1n), which is the same as R. asanoi sensu e.g. Raffi et al. (2006). Their data also shows that large P. ovata specimens increase in abundance during this interval. So, yes R. asanoi will intergrade with smaller oval Reticulofenestra species and with P. ovata specimens with a few slits, but it is still useful to distinguish it.

Matsuoka, H. & Okada, H. 1989. Quantitative Analysis of Quaternary Nanoplankton in the Subtropical Northwestern Pacific Ocean. Marine Micropaleontology 14, 97- 118.
Raffi, I., Backman, J., Fornaciari, E., Palike, H., Rio, D., Lourens, L. J. & Hilgen, F. J. 2006. A review of calcareous nannofossil astrobiochronology encompassing the past 25 million years. Quaternary Science Reviews 25, 3113-3137. 
Young, J. R. 1990. Size variation of Neogene Reticulofenestra coccoliths from Indian Ocean DSDP cores. Journal of Micropalaeontology 9, 71-86.
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